[setrofim_]

>Is the color->note map arbitrary or is there some logic behind it?

One way of doing this would be to map from the electromagnetic wavelength of the color to a corresponding audible frequency.

Audible range is something like 32 to 32768 Hrz. Assuming speed of sound in air of 343 m/s, this translates to wavelength range of 0.010437 to 10.6875 m . This can then be mapped onto the visible spectrum of 390 to 750 nm.

light_range = (750 * 10^-9) - (390 * 10^-9)

sound_range = 10.6875 - 0.010437

light_wavelength = (light_range * ((343 / sound_freq) - 0.010437) / sound_range) + (390 * 10^-9)